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                <h1 id="JVM内存和垃圾回收篇"><a href="#JVM内存和垃圾回收篇" class="headerlink" title="JVM内存和垃圾回收篇"></a>JVM内存和垃圾回收篇</h1><blockquote>
<p>JVM内存和垃圾回收篇<br>字节码与类的加载篇<br>性能监控与调优篇</p>
</blockquote>
<h2 id="概述"><a href="#概述" class="headerlink" title="概述"></a>概述</h2><p><img src="https://s1.ax1x.com/2020/09/23/wxKNSe.png" alt="一次编译到处运行"></p>
<p><strong>任何语言编译后的字节码文件遵守java虚拟机规范，都可以运行在java虚拟机上</strong></p>
<p><img src="https://s1.ax1x.com/2020/09/23/wxKuQJ.png" alt="任何语言都可以运行在jvm上"></p>
<p>多语言混合开发不再是不可能的事情。</p>
<blockquote>
<p>java虚拟机就是二进制字节码的运行环境，负责装在字节码到其内部，解释编译为对应平台的机器指令执行。</p>
</blockquote>
<p><img src="https://s1.ax1x.com/2020/09/23/wxKAoV.png" alt="jdk-jre-jvm"></p>
<h3 id="JVM的整体结构"><a href="#JVM的整体结构" class="headerlink" title="JVM的整体结构"></a>JVM的整体结构</h3><p><img src="https://s1.ax1x.com/2020/09/23/wxuoxH.png" alt="JVM简图"></p>
<h3 id="JVM的架构模型"><a href="#JVM的架构模型" class="headerlink" title="JVM的架构模型"></a>JVM的架构模型</h3><p><img src="https://s1.ax1x.com/2020/09/23/wxu1PS.png" alt="架构模型"></p>
<p><strong>总结</strong></p>
<ul>
<li>跨平台性的设计</li>
<li>指令集小</li>
<li>指令多</li>
<li>执行性能比寄存器差</li>
</ul>
<h3 id="JVM的生命周期"><a href="#JVM的生命周期" class="headerlink" title="JVM的生命周期"></a>JVM的生命周期</h3><p><strong>虚拟机的启动</strong></p>
<p>java虚拟机的启动时通过<strong>引导类加载器</strong>(bootstrap class loader)创建一个初始类(initial class)来完成的，这个类是由虚拟机的具体实现指定的。</p>
<p><strong>虚拟机的运行</strong></p>
<ul>
<li>一个运行中的java虚拟机有一个任务就是执行java程序</li>
<li>程序开始执行时他才运行，程序结束的时候他就停止</li>
<li>==执行一个所谓的java程序的时候，真正在执行的是JAVA虚拟机的进程==</li>
</ul>
<p><strong>虚拟机的退出</strong></p>
<ul>
<li>程序正常执行结束</li>
<li>遇到异常或错误终止</li>
<li>操作系统出现错误导致java虚拟机进程终止</li>
<li>某线程调用runtime类或system类的exit方法退出，或runtime类中的halt方法</li>
<li>JNI规范描述了用JNI Invocation API来加载或卸载Java虚拟机的时候，jvm退出</li>
</ul>
<h2 id="类加载子系统-ClassLoader"><a href="#类加载子系统-ClassLoader" class="headerlink" title="类加载子系统(ClassLoader)"></a>类加载子系统(ClassLoader)</h2><blockquote>
<p><strong>整体作用</strong></p>
<ul>
<li><p>负责从文件系统或网络中加载class文件，class文件在文件开头有特定的文件标识</p>
</li>
<li><p>ClassLoader只负责class文件的加载，至于它是否可以运行，则由Execution Engine决定</p>
</li>
<li><p>加载的类信息存放于一块称为==方法区==的内存空间。除了类的信息外，方法区中还会存放运行时常量池信息，可能还包括字符串字面量和数字常量(这部分常量信息是Class文件中常量池部分的内存映射)</p>
</li>
</ul>
</blockquote>
<p><img src="https://s1.ax1x.com/2020/09/23/wxueKA.png" alt="类加载子系统"></p>
<ul>
<li><p>class文件放在本地的硬盘上，当执行的时候是要加载到JVM中，根据这个文件实例化出n个一模一样的实例。</p>
</li>
<li><p>class文件加载到JVM中，被称为DNA元数据模板，放在方法区</p>
</li>
<li><p>在.class文件-&gt;JVM-&gt;最终称为元数据模板，此过程就要一个运输工具(类装载器 ClassLoader)扮演一个快递员的角色</p>
</li>
</ul>
<p><img src="https://s1.ax1x.com/2020/09/23/wxuA8e.png" alt="wxuA8e.png"></p>
<h3 id="类的加载过程"><a href="#类的加载过程" class="headerlink" title="类的加载过程"></a>类的加载过程</h3><p><strong>加载阶段</strong></p>
<blockquote>
<ul>
<li>通过一个类的全限定名获取定义此类的二进制文件流</li>
<li>将这个字节流所代表的静态存储结构转化为方法区的运行时数据结构（<strong>类信息放在方法区中</strong>）</li>
<li>==在内存中生成一个代表这个类的java.lang.Class对象==，作为方法区这个类的各种数据的访问入口（<strong>反射</strong>放在堆中）</li>
</ul>
</blockquote>
<p><strong>链接阶段</strong></p>
<ul>
<li><p>验证</p>
<blockquote>
<ul>
<li>目的在于确保class文件袋字节流中包含的信息符合当前虚拟机要求，保证被加载类的正确性</li>
<li>文件格式验证，元数据验证，字节码验证，符号引用验证</li>
</ul>
</blockquote>
</li>
<li><p>准备</p>
<blockquote>
<ul>
<li>为类变量分配内存并且设置该类变量的默认初始值，即零值<ul>
<li><code>private static int a = 1</code>在准备阶段会被先设为<code>a=0</code>，在<code>initial</code>阶段才会赋值</li>
</ul>
</li>
<li><strong>这里不含用final修饰的static,因为final在编译的时候就分配了，准备阶段会显式初始化</strong>（<strong>这时候是常量了</strong>）</li>
<li><strong>这里不会为实例变量分配初始化</strong>（还未创建对象），类变量会分配在方法区中，而实例变量是会随着对象一起分配到java堆中</li>
</ul>
</blockquote>
</li>
<li><p>解析</p>
<blockquote>
<ul>
<li>将常量池内的符号引用转换为直接引用的过程</li>
<li>事实上，解析操作会在JVM执行完初始化后再次执行</li>
<li>符号引用就是一组符号来描述引用的目标。直接引用就是直接指向目标的指针，相对偏移量或一个间接定位到目标的句柄</li>
<li>解析主要针对：类或接口，字段，类方法，接口方法，方法类型等等，对应常量池中的CONSTANT_Class_info、CONSTANT_Fieldref_info、CONSTANT_Methodref_info 等等</li>
</ul>
</blockquote>
</li>
</ul>
<p><strong>初始化</strong></p>
<blockquote>
<ul>
<li>初始化就是执行<strong>类构造器方法<Clinit>()**的过程，<Clinit>()不需要定义，他不是类的构造器，javac编译器自动帮你弄好了。</strong>构造器方法中指令按照语句在源文件中出现的顺序执行**。JVM会保证子类的<Clinit>()执行前，父类的<Clinit>()方法已经执行完毕。</li>
<li><strong>类构造器是对静态变量，静态代码块进行初始化</strong></li>
</ul>
</blockquote>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">class</span> <span class="token class-name">X</span> <span class="token punctuation">&#123;</span>
   <span class="token keyword">static</span> <span class="token class-name">Log</span> log <span class="token operator">=</span> <span class="token class-name">LogFactory</span><span class="token punctuation">.</span><span class="token function">getLog</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// &lt;clinit></span>
   <span class="token keyword">private</span> <span class="token keyword">int</span> x <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span>   <span class="token comment">// &lt;init></span>
   <span class="token class-name">X</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
      <span class="token comment">// &lt;init></span>
   <span class="token punctuation">&#125;</span>
   <span class="token keyword">static</span> <span class="token punctuation">&#123;</span>
      <span class="token comment">// &lt;clinit></span>
   <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>


<p>​        类中的类变量和静态代码块中的语句会被编译器自动收集，收集的顺序是由语句在源文件中出现的顺序决定的。如下图所示，，num变量和number变量在prepare阶段的时候被赋值为0，到initial阶段会按照顺序，先将num赋值为1,再执行static代码块中的<code>num=2</code>赋值为2。</p>
<p>​        而对于number来说，虽然他定义语句是在静态代码块下边，静态代码块中对他进行了赋值，但是他被创建分配内存是在prepare阶段，所以按照顺序会先把他赋值为<code>20</code>,再赋值为<code>10</code>。</p>
<p>​        但是如果在静态代码块中提前访问number的话会报错，<strong>非法的前向引用</strong>。可能是在JVM执行完初始化后还会再次解析，把他的符号引用改为直接引用？？？—-这一点是个人猜测</p>
<p><img src="https://s1.ax1x.com/2020/09/23/wxuPUK.png" alt="wxuPUK.png"></p>
<p><img src="https://s1.ax1x.com/2020/09/23/wxuSD1.png" alt="wxuSD1.png"></p>
<p>总结：</p>
<p><img src="https://s1.ax1x.com/2020/09/23/wxnvv9.png" alt="wxnvv9.png"></p>
<h3 id="类加载器分类"><a href="#类加载器分类" class="headerlink" title="类加载器分类"></a>类加载器分类</h3><blockquote>
<p>jvm支持两种类型的加载器</p>
<ul>
<li>引导类加载器（Bootstrap ClassLoader）</li>
<li>自定义加载器（User-Defined ClassLoader）<ul>
<li>拓展类加载器</li>
<li>系统类加载器</li>
</ul>
</li>
</ul>
<p>只要是派生于抽象类ClassLoader的加载器，就是自定义加载器</p>
</blockquote>
<p><img src="https://s1.ax1x.com/2020/09/23/wxnbNT.png" alt="wxnbNT.png"></p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">        <span class="token comment">// 获取系统类加载器</span>
        <span class="token class-name">ClassLoader</span> systemClassLoader <span class="token operator">=</span> <span class="token class-name">ClassLoader</span><span class="token punctuation">.</span><span class="token function">getSystemClassLoader</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"classLoader = "</span> <span class="token operator">+</span> systemClassLoader<span class="token punctuation">)</span><span class="token punctuation">;</span>
        
        <span class="token comment">// 获取上层拓展类加载器</span>
        <span class="token class-name">ClassLoader</span> extClassLoader <span class="token operator">=</span> systemClassLoader<span class="token punctuation">.</span><span class="token function">getParent</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"extClassLoader = "</span> <span class="token operator">+</span> extClassLoader<span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token comment">// 获取其上层：获取不到引导类加载器</span>
        <span class="token class-name">ClassLoader</span> bootStrapClassLoader <span class="token operator">=</span> extClassLoader<span class="token punctuation">.</span><span class="token function">getParent</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"bootStrapClassLoader = "</span> <span class="token operator">+</span> bootStrapClassLoader<span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// 获取当前的类加载器</span>
        <span class="token class-name">ClassLoader</span> classLoader <span class="token operator">=</span> <span class="token class-name">ClassLoaderTest</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">.</span><span class="token function">getClassLoader</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"classLoader = "</span> <span class="token operator">+</span> classLoader<span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// 获取不到引导类加载器，java的核心类库是用引导类加载器加载的</span>
        <span class="token class-name">ClassLoader</span> classLoader1 <span class="token operator">=</span> <span class="token class-name">String</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">.</span><span class="token function">getClassLoader</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"classLoader1 = "</span> <span class="token operator">+</span> classLoader1<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">/*
出于安全考虑，Bootstrap启动类加载器只加载包名为 java、javax、sun等开头的类
*/</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>


<h3 id="启动类加载器"><a href="#启动类加载器" class="headerlink" title="启动类加载器"></a>启动类加载器</h3><blockquote>
<p>也是引导类加载器，bootStrap ClassLoader 是用c++写的，所以看不到源码。</p>
<p>它负责将 <JAVA_HOME>/lib目录、 -Xbootclasspath选项指定的目录或系统属性sun.boot.class.path指定的目录下的核心类库加载到内存中。 </p>
<p>出于安全考虑，Bootstrap启动类加载器只加载包名为 java、javax、sun等开头的类</p>
</blockquote>
<h3 id="拓展类加载器"><a href="#拓展类加载器" class="headerlink" title="拓展类加载器"></a>拓展类加载器</h3><blockquote>
<p>sun.misc.Launcher$ExtClassLoader实现</p>
<p>派生于ClassLoader</p>
<p>父类加载器为启动类加载器</p>
<p>从java.ext.dirs系统属性所指定的目录中加载类库，或从jdk的安装目录的jre/lib/ext子目录下加载类库。如果用户创建的jar放在此目录下，也会自动由拓展累加载器加载</p>
</blockquote>
<h3 id="应用程序类加载器"><a href="#应用程序类加载器" class="headerlink" title="应用程序类加载器"></a>应用程序类加载器</h3><blockquote>
<p>也叫系统类加载器,ApplicationClassLoader</p>
<p>派生于ClassLoader类</p>
<p>父类是拓展类加载器</p>
<p>负责加载环境变量classpath或系统属性java.class.path指定路径下单类库，该类加载是<strong>程序中默认的累加载器</strong></p>
<p>通过ClassLoader#getSystemClassLoader方法可以获取到该类加载器</p>
</blockquote>
<h3 id="用户自定义类加载器"><a href="#用户自定义类加载器" class="headerlink" title="用户自定义类加载器"></a>用户自定义类加载器</h3><blockquote>
<ul>
<li>为何要使用？<ul>
<li>隔离加载类</li>
<li>修改类加载方式</li>
<li>拓展加载源</li>
<li>防止源码泄漏(运行时解密)</li>
</ul>
</li>
</ul>
</blockquote>
<p>获取加载类内容</p>
<p><img src="/home/zhy/.config/Typora/typora-user-images/image-20200924092057934.png" alt="image-20200924092057934"></p>
<h2 id="双亲委派机制！（重点）"><a href="#双亲委派机制！（重点）" class="headerlink" title="双亲委派机制！（重点）"></a>双亲委派机制！（重点）</h2><blockquote>
<p>java虚拟机对class文件采用的是按需加载的方式，而加载某个类的class文件时，java虚拟机采用的是<strong>双亲委派模式</strong>，即把请求交由父类处理，他是一种任务委派模式</p>
</blockquote>
<p>引入：我们自己构造一个String类</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token comment">/*在项目src下创建java.lang.String*/</span>
<span class="token keyword">package</span> <span class="token namespace">java<span class="token punctuation">.</span>lang</span><span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">String</span> <span class="token punctuation">&#123;</span>
    <span class="token punctuation">&#123;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"测试双亲委派机制，自制String类"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>我们创建一个测试类来调用新创建的String类，测试能否把静态代码块中的值输出</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">package</span> <span class="token namespace">com<span class="token punctuation">.</span>study</span><span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">StringTest</span> <span class="token punctuation">&#123;</span>

    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token comment">// 在这里new我们创建的类</span>
        <span class="token class-name"><span class="token namespace">java<span class="token punctuation">.</span>lang<span class="token punctuation">.</span></span>String</span> str <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name"><span class="token namespace">java<span class="token punctuation">.</span>lang<span class="token punctuation">.</span></span>String</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"测试类"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>运行结果：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token operator">/</span>usr<span class="token operator">/</span>local<span class="token operator">/</span>java<span class="token operator">/</span>jdk1<span class="token punctuation">.</span><span class="token number">8.0_191</span><span class="token operator">/</span>bin<span class="token operator">/</span>java <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
测试类

<span class="token class-name">Process</span> finished <span class="token keyword">with</span> <span class="token namespace">exit</span> code <span class="token number">0</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span></span></code></pre>
<blockquote>
<p>我们可以发现，程序没有走我们自制的String类，，其中就是运用了<strong>双亲委派机制</strong></p>
</blockquote>
<h3 id="工作原理"><a href="#工作原理" class="headerlink" title="工作原理"></a>工作原理</h3><ol>
<li>如果一个类加载器收到了类加载请求，它并不会自己先去加载，而是把这个请求委托给父类的加载器去执行</li>
<li>如果父类加载器还存在其父类加载器，进一步向上委托，依次递归，请求最终将达到顶层的Bootstrap ClassLoader启动类加载器</li>
<li>如果父类加载器可以完成类加载任务，就返回成功，倘若父类加载器无法完成此加载任务，子加载器才会尝试自己去加载</li>
</ol>
<p><img src="/home/zhy/.config/Typora/typora-user-images/image-20200924094613781.png" alt="双亲委派机制"></p>
<p><strong>当我们在自定义的String中编写main方法的时候</strong>，因为双亲委派机制，会加载Java中的String，但是他里边没有main方法，就会报错</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">String</span> <span class="token punctuation">&#123;</span>
    <span class="token punctuation">&#123;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"测试双亲委派机制，自制String类"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
	
    <span class="token comment">/*
    错误: 在类 java.lang.String 中找不到 main 方法, 请将 main 方法定义为:
  	public static void main(String[] args)
	否则 JavaFX 应用程序类必须扩展javafx.application.Application
    */</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token number">12312</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>


<p>第三方jar包的加载会由系统类加载器去加载，在图中是由线程上下文类加载器(ContextClassLoader)加载的</p>
<p>可以看这篇博客–&gt;<a target="_blank" rel="noopener" href="https://blog.csdn.net/yangcheng33/article/details/52631940">https://blog.csdn.net/yangcheng33/article/details/52631940</a></p>
<p><img src="/home/zhy/.config/Typora/typora-user-images/image-20200924102029562.png" alt="第三方jar包的加载"></p>
<blockquote>
<p>双亲委派机制的<strong>优势</strong></p>
<ul>
<li><strong>避免类重复加载</strong></li>
<li><strong>保护程序安全，防止核心Api被篡改</strong><ul>
<li>自制java.lang.String类</li>
</ul>
</li>
</ul>
</blockquote>
<p><strong>沙箱安全机制</strong></p>
<blockquote>
<p>自定义String类在加载的时候会让引导类加载器去加载jdk下的String类，这样由于没有main方法，会报错<code>在类 java.lang.String 中找不到 main 方法, 请将 main 方法定义为:public static void main(String[] args)</code>。这样可以保证对java核心源代码的保护，这就是<strong>沙箱安全机制</strong></p>
</blockquote>
<h3 id="类的主动使用和被动使用"><a href="#类的主动使用和被动使用" class="headerlink" title="类的主动使用和被动使用"></a>类的主动使用和被动使用</h3><blockquote>
<p>主动使用</p>
</blockquote>
<p><img src="/home/zhy/.config/Typora/typora-user-images/image-20200924110708399.png" alt="image-20200924110708399"></p>
<blockquote>
<p>除了上述的7种，都是<strong>被动使用</strong>，都不会<strong>导致类的初始化</strong></p>
</blockquote>

                
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